The present invention relates to a device for cannulation of a hollow organ, said device comprising a cannula that has a proximal end, a distal end, and a central section located between the proximal end and distal end, and the cannula, after introduction into the vessel, is in fluid communication with the vessel.
Devices of this kind that comprise a cannula are used in a variety of ways in the surgical and medical field, for example for cannulation of arterial or venous blood vessels. A typical cannula is a small tube which in most cases has a fixed diameter and which a surgeon or physician uses in order to withdraw blood or in order to create a passage for blood between a patients' circulation and an extracorporeal system. Thus, an extracorporeal circuit, for example for extracorporeal blood oxygenation, can be maintained by a blood pump, or, if the endogenous blood pressure is used, without a pump. Extracorporeal lung assist (iLA, AVCO2R, pECLA, ECMO, etc.) is used in patients with acute lung failure in whom, while avoiding the risks of conventional ventilation, carbon dioxide is removed from the blood and oxygen enrichment takes place. The oxygen-rich blood is then returned to the patient. To do this, two individual cannulas or a double-lumen cannula are introduced into peripheral vessels, after which the blood flows via a short hose system through what is called a membrane lung and then back into the patient's circulation. In intensive care medicine, cannulas are inserted, for example, through a peripheral vessel of the leg or neck. This system has the advantage that a sufficient gas exchange can be achieved over a period of days or even weeks, as a result of which it is possible to avoid aggressive forms of ventilation, for example, and ventilator-associated lung injury (VALI), and the lung is able to regenerate.
Cannulas of different dimensions and diameters can be used depending on the vessel, in particular depending on the latter's size. Flexible catheters or cannulas usually have a fixed lumen and a fixed size in terms of their external diameter. In a heart-lung bypass, for example, a large lumen has to be provided in order to permit a sufficient flow of oxygenated blood. For this purpose, a traditional catheter or a cannula must have a large diameter, which in turn makes it difficult to insert the cannula/catheter into the vessel, in particular to pass it through tissue, and can lead to a surgical intervention that entails greater damage to the surrounding tissue.
In cannulation of arterial vessels with small cannulas, the smaller diameter of the lumen means that the resistance of the blood flow inside the cannula increases, which has the result of limiting the flow rate. High flow rates are enforced when blood pumps are used, and the resulting high shearing stresses in the blood stream represent a danger of damage to blood cells.
Larger cannulas, on the other hand, permit higher flow rates with at the same time less stress on the blood. However, the danger of using larger cannulas is that the blood vessel is closed after introduction of the cannula, and the physiological flow conditions in other areas of the circulation are disturbed. For example, when access is made into an arterial vessel, the physiological flow of blood in the downstream blood circulation, for example in the extremities or in other organs, may be prevented. This blocking of the flow of blood there can lead to ischaemia, an imbalance between oxygen and nutrient demand and supply, with consequent necrosis of the affected tissue. Moreover, cannulation of a venous vessel can cause congestion of the flow of blood back to the heart, with resulting organ damage and the danger of coagulation.
Because of the dangers outlined above, it is therefore important to determine the size of the cannula in a pumpless extracorporeal circuit with arterio-venous connection, and similarly in a veno-venous or veno-arterial extracorporeal circuit with blood pump. As has been mentioned above, the flow rate of the blood in the absence of a pump is dependent on the physiological blood pressure conditions in the circulation, on the size of the cannula, and on the resistance of the extracorporeal system (artificial lung, haemofilter, hoses, etc.).
To achieve higher flow rates of blood, cannulas with a large lumen are required, but this may again entail the abovementioned disadvantage of ischaemia or venous blood congestion.
Since the blood pressure in the venous circulation is low, pressure has to be built up to permit active venous drainage for the extracorporeal circuit, and this is achieved by using a pump. At high flow rates of blood through the cannula, the blood pressure may drop, thus leading to an underpressure in the vessel. This can lead to collapse of the vessel, since the vessel walls are pressed inward by the pressure prevailing outside the vessel, which leads to occlusion of the vessel and to interruption of the blood flow.
Therefore, the diameter and the length of the venous cannula, as a function of the desired flow of blood, are also important considerations in the case of venous blood supply into an extracorporeal circuit with veno-venous or veno-arterial connection. For example, it also determines the extent or the avoidance of blood trauma caused by underpressure and resulting excessive shearing forces.
The prior art discloses cannulas whose lumen can be widened along their entire length, and cannulas which additionally have an occlusion balloon at one end.
Thus, U.S. Pat. No. 6,613,038 B2 discloses a cannula which is inserted through the tissue in a non-expanded state with a small diameter, and which, after removal of a cannula sleeve, then expands radially outwards along its entire length as soon as it has been inserted into the desired vessel or tissue.
Moreover, U.S. Pat. No. 6,679,871 discloses a cannula which, along the length of its lumen, has an inflatable balloon that can be expanded after introduction into a blood vessel. This catheter can further comprise an occlusion balloon which, after its expansion, completely closes the vessel.
However, the abovementioned embodiments of cannulas are not able to overcome the problems known in the prior art, since with these cannulas too there is a danger of the vessel becoming occluded and, in an arterial application, of the flow of blood in the extremities being prevented.